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The development of technologies for the removal of dye from aqueous solution is most desirable if the end product is relatively green (i.e., environmentally friendly). Photodegradation (as one of such technology) and photolysis (without the catalyst) was applied to investigate the role of sol-gel synthesized calcium oxide nanoparticle (using the oyster shell as the precursor). The results obtained gave substantial evidence that calcium oxide nanoparticles catalyzed the degradation of the methylene blue dye up to a maximum percentage of 98 % removal. Degradation efficiency displayed a strong dependency on time, initial dye concentration, catalyst load, pH, and ionic strength. Chi-square and sum of square error analysis indicated that the photodegradation kinetics fitted the Langmuir-Hinshelwood, first order, and pseudo first-order models best. The half-life of the dye was significantly reduced from hours to minutes due to photocatalysis. Quantum chemical calculations indicated that the degradation proceeded through adsorption, deformation/degradation, and desorption through the chloride end of the molecule linked to the calcium active center of the catalyst. Results from Fukui functions and molecular descriptors analysis confirmed the mechanism of photocatalysis. Graphical abstract

Water pollution is a significant issue worldwide due to an increase in anthropogenic activities. Heavy metals and dyes are among the most problematic contaminants that threaten the environment and negatively impact human health. Iron oxide nanoparticles (IONPs) synthesized using green methods have shown potential in these areas due to their significant adsorption capacity and photocatalytic potential. The size and morphology of biogenic IONPs can be tailored depending upon the concentration of the reducing medium and metal salt precursor. Green-synthesized IONPs have been found to be effective, economical, and environmentally friendly with their large surface area, making them suitable for removing toxic matter from contaminated water. Furthermore, they exhibit antibacterial potential against harmful microorganisms. The study emphasizes the importance of using such environmentally friendly tools to remove heavy metal ions and organic compounds from contaminated water. The underlying mechanism for the adsorption of heavy metal ions, photocatalytic degradation of organic compounds, and antimicrobial action has been explored in detail. The future prospective for the beneficial utilization of biogenic IONPs has also been signified to provide a detailed overview.

The sequestration of contaminants from wastewater, such as heavy metals, has become a major global issue. Multiple technologies have been developed to address this issue. Nanotechnology is attracting significant interest as a new technology, and numerous nanomaterials have been produced for sequestrating heavy metals from polluted water due to their superior properties arising from the nanoscale effect. This study reports biosynthesis of iron oxide nanoparticles (IO-NPs) and their applications for adsorptive sequestration of various metal ions from aqueous solutions. Biosynthesis of IO-NPs has been carried out by using leaf extract of Spilanthes acmella , a medicinal plant. FTIR analysis of the leaf extract and biosynthesized IO-NPs marked the role of various functional groups in biosynthesis of IO-NPs. FESEM analysis revealed the average size range of IO-NPs as 50 to 80 nm, while polydisperse nature was confirmed by DLS analysis. EDX analysis revealed the presence of Fe, O, and C atoms in the elemental composition of the NPs. The antioxidant potential of the biosynthesized IO-NPs (IC 50  = 136.84 µg/mL) was confirmed by DPPH assay. IO-NPs were also used for the adsorptive removal of As 3+ , Co 2+ , Cd 2+ , and Cu 2+ ions from aqueous solutions with process optimization at an optimized pH (7.0) using dosage of IO-NPs as 0.6 g/L (As 3+ and Co 2+ ) and 0.8 g/L (Cd 2+ and Cu 2+ ). Adsorption isotherm analysis revealed the maximum adsorption efficiency for As 3+ (21.83 mg/g) followed by Co 2+ (20.43 mg/g), Cu 2+ (15.29 mg/g), and Cd 2+ (13.54 mg/g) using Langmuir isotherm model. The biosynthesized IO-NPs were equally efficient in the simultaneous sequestration of these heavy metal ions signifying their potential as effective nanoadsorbents.

Three thiosemicarbazides, namely 2-(2-aminophenyl)-N phenylhydrazinecarbothioamide (AP4PT), N,2-diphenylhydrazinecarbothioamide (D4PT) and 2-(2-hydroxyphenyl)-N-phenyl hydrazinecarbothioamide (HP4PT), were investigated as corrosion inhibitors for mild steel in H2SO4 solution using gravimetric and gasometric methods. The results revealed that they all inhibit corrosion and their % inhibition efficiencies (%IE) follow the order: AP4PT > HP4PT > D4PT. The %IE obtained from the gravimetric and gasometric experiments were in good agreement. The thermodynamic parameters obtained support a physical adsorption mechanism and the adsorption followed the Langmuir adsorption isotherm. Some quantum chemical parameters were calculated using different methods and correlated with the experimental %IE. Quantitative structure activity relationship (QSAR) approach was used on a composite index of some quantum chemical parameters to characterize the inhibition performance of the studied molecules. The results showed that the %IE were closely related to some of the quantum chemical parameters, but with varying degrees. The calculated/theoretical %IE of the molecules were found to be close to their experimental %IE. The local reactivity has been studied through the Fukui and condensed softness indices in order to predict both the reactive centers and to know the possible sites of nucleophilic and electrophilic attacks.

Introduction: Medicinal plants contain essential phytochemicals and are used in traditional herbal therapy for ages. These phytochemicals are bioactive compounds and possess significant antibacterial and antifungal properties in addition to more biologically important potentials. The important bioactive phytochemicals include polyphenolic compounds and flavonoids. Arisaema tortuosum has been reported as a medicinal plant in literature and is used in treating many health issues. Aim: To investigate the phytochemical composition, total polyphenolic content (TPC), total flavonoid content (TFC), antioxidant capacity, and β-glucuronidase inhibition potential of the extract obtained from leaves of A. tortuosum. Methods: The phytochemical composition, TPC, TFC, and antioxidant capacity of the extract was analysed. β-glucuronidase inhibition assay was used to determine β-glucuronidase inhibition potential. The dose-dependent data was used to determine IC50 value of the extract. Results: The gas chromatography-mass spectroscopy (GC-MS) analysis identified the fifty-three components from the leaf extract that was observed to possess a significant volume of TPC and TFC. 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assay revealed a IC50 value of 936 μg/mL indicating a high antioxidant activity of the extract. Conclusion: The study revealed the presence of many biologically important phytochemicals and a rich number of total polyphenols and flavonoids in leaf extract of A. tortuosum signifying the potential biomedical applications. Introducción: las plantas medicinales contienen compuestos fitoquímicos esenciales y se utilizan en la terapia herbolaria tradicional desde hace siglos. Estos fitoquímicos son compuestos bioactivos y poseen importantes propiedades antibacterianas y antifúngicas, además de potenciales efectos biológicamente más importantes. Los fitoquímicos bioactivos importantes incluyen compuestos polifenólicos y flavonoides. En la literatura se ha reportado a la Arisaema tortuosum como una planta medicinal y que se usa para tratar muchos problemas de salud. Objetivo: investigar la composición fitoquímica, el contenido polifenólico total (TPC), el contenido total de flavonoides (TFC), la capacidad antioxidante y el potencial de inhibición de la β-glucuronidasa del extracto obtenido de las hojas de A. tortuosum. Métodos: se analizó la composición fitoquímica, TPC, TFC y la capacidad antioxidante del extracto. Se utilizó el ensayo de inhibición de β-glucuronidasa para determinar el potencial de inhibición de este agente. Los datos dependientes de la dosis se usaron para determinar el valor IC50 del extracto. Resultados: el análisis de cromatografía de gases-espectroscopía de masas (GC-MS) permitió identificar cincuenta y tres componentes del extracto de hojas, que se observó que poseían un volumen significativo de TPC y TFC. El ensayo de 1,1-difenil-2-picril-hidrazilo (DPPH) reveló un valor IC50 de 936 μg/mL, lo que indica una alta actividad antioxidante del extracto. Conclusión: este estudio reveló la presencia de muchos compuestos fitoquímicos biológicamente importantes y una gran cantidad de polifenoles totales y flavonoides en el extracto de hoja de A. tortuosum, lo que significa aplicaciones biomédicas potenciales. Introdução: as plantas medicinais contêm compostos fitoquímicos essenciais e têm sido utilizadas na terapia tradicional à base de plantas há séculos. Esses fitoquímicos são compostos bioativos e possuem importantes propriedades antibacterianas e antifúngicas, além de efeitos potencialmente mais importantes biologicamente. Fitoquímicos bioativos importantes incluem compostos polifenólicos e flavonóides. Arisaema tortuosum tem sido relatada na literatura como planta medicinal e utilizada para o tratamento de diversos problemas de saúde. Objetivo: investigar a composição fitoquímica, teor de polifenóis totais (TPC), teor de flavonoides totais (TFC), capacidade antioxidante e potencial de inibição da β-glucuronidase do extrato obtido das folhas de A. tortuosum. Métodos: foram analisados a composição fitoquímica, TPC, TFC e a capacidade antioxidante do extrato. O ensaio de inibição da β-glucuronidase foi utilizado para determinar o potencial de inibição deste agente. Os dados dependentes da dose foram usados para determinar o valor IC50 do extrato. Resultados: a análise por cromatografia gasosa-espectroscopia de massa (GC-MS) permitiu a identificação de cinquenta e três componentes do extrato da folha, que apresentaram um volume significativo de TPC e TFC. O ensaio de 1,1-difenil-2-picril-hidrazil (DPPH) revelou um valor de IC50 de 936 μg/ mL, indicando uma alta atividade antioxidante do extrato. Conclusão: este estudo revelou a presença de muitos compostos fitoquímicos biologicamente importantes e uma grande quantidade de polifenóis totais e flavonóides no extrato da folha de A. tortuosum, significando potenciais aplicações biomédicas.

The corrosion inhibition of ampicillin (AMP) and its synergistic combination with halides (KI, KCl and KBr) for the corrosion of mild steel in H2SO4 have been investigated using gravimetric, gasometric, thermometric and infrared (IR) methods. The inhibition efficiencies of AMP for the corrosion of mild steel increased with increase in concentration but decreased with rise in temperature. The adsorption of AMP on the mild steel surface was found to obey the Langmuir adsorption isotherm model. The combination of AMP with the halides (KI, KBr and KCl) enhanced the inhibition efficiency and adsorption behavior of the inhibitor indicating synergism. The inhibition efficiency of AMP increased with increasing concentration and the adsorption of the inhibitor was spontaneous. Physical adsorption mechanism has been proposed from the thermodynamic data obtained. There was a significant correlation between the inhibition efficiency of AMP and some quantum chemical parameters (R2 = 0.96) using the quantitative structure–activity relationship (QSAR) method. Some quantum chemical parameters and the Mulliken charge densities on the optimized structure of AMP were calculated using the B3LYP/6-31G (d,p) basis set method to provide further insight into the mechanism of the corrosion inhibition process.

The corrosion of metals, i.e., the initiation and acceleration of the surface deterioration of metals through an electrochemical reaction with the surrounding intrusive environment, is a global concern because of the economic and environmental impacts. Corrosion inhibitors are considered the most practical choice among the available corrosion protection techniques due to their effectiveness in terms of functionality and cost. The use of traditional and toxic corrosion inhibitors has led to environmental issues, arousing the need for green counterparts that are environmentally friendly, easily accessible, biodegradable, and cost-effective. In this review, the utilization of green corrosion inhibitors purely acquired from renewable sources is explored, with an in-depth focus on the recent advancements in the use of fruit and vegetable extracts as green corrosion inhibitors. In particular, fruits and vegetables are natural sources of various phytochemicals that exhibit key potential in corrosion inhibition. To shed light on the true potential of such extracts in the protection of steel in acidic environments, the experimental techniques involved in corrosion inhibition and the mechanism of corrosion inhibition are discussed in detail. The study highlights the potential of fruit and vegetable extracts as non-toxic, economical, and effective corrosion inhibitors in the pursuit of green chemistry. In addition to discussing and outlining the current status and opportunities for employing fruit and vegetable extracts as corrosion inhibitors, the current review outlines the challenges involved in the utilization of such extracts in corrosion inhibition.

Experimental aspects of the inhibition of the corrosion of mild steel in HCl solutions by some carbozones were studied using gravimetric, thermometric and gasometric methods, while a theoretical study was carried out using density functional theory, a quantitative structure–activity relation, and quantum chemical principles. The results obtained indicated that the studied carbozones are good adsorption inhibitors for the corrosion of mild steel in HCl. The inhibition efficiencies of the studied carbozones were found to increase with increasing concentration of the respective inhibitor. A strong correlation was found between the average inhibition efficiency and some quantum chemical parameters, and also between the experimental and theoretical inhibition efficiencies (obtained from the quantitative structure–activity relation).

The inhibition of the corrosion of mild steel in 0.1 M H 2 SO 4 by 3-nitrobenzoic acid was studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization resistant, potentiodynamic polarization, scanning electron microscopy, Fourier transformed infra-red spectroscopy and quantum chemical techniques. The results obtained indicated that 3-nitrobenzoic acid inhibited the corrosion of mild steel in solution of H 2 SO 4 . Maximum inhibition efficiency obtained from weight loss, potentiodynamic, linear polarization and EIS methods were 87.15, 90.51, 95.42 and 99.40% at inhibitor's concentration of 0.01 M respectfully. The activation energies (which ranged from 26.02 to 59.02 J/mol) supported the mechanism of charge transfer from charged inhibitor to charged metal surface, which favours the mechanism of physical adsorption. The adsorption of the inhibitor was found to be exothermic and spontaneous. Although the adsorption characteristics of the inhibitor fitted the Langmuir adsorption model, the deviation of slope values from unity was explained by the existent of positive interaction parameters (attractive behaviour of the inhibitor's molecules) according to the Frumkin model. 3-nitrobenzoic acid is dominantly a cathodic-type inhibitor and prevented the corrosion of mild steel by blocking the metal's surface. Calculated values of the frontier molecular orbital energies and other semi-empirical parameters were in good agreement with those obtained for known and efficient corrosion inhibitors while Fukui function analysis indicated that the inhibitor is adsorbed unto the metal surface through the delocalization of electrons in the nitro oxygen bond, i.e. O(11)-N(10)-O(12).

Citrus fruits are a valuable source that consists of bioactive phytochemicals with a balanced composition. Citrus by-products are, however, disposed of in large quantities and are not being appropriately used. This is a review of the phytochemistry, sustainable processing, and use of this biomass across various industrial sectors. The problem of uneven distribution of bioactives (flavonoids, limonoids, essential oils, and pectin) in citrus fruit, peels, and seeds has been addressed. The different extraction methods are compared, and green methods are emphasized as more effective for extraction and less harmful to the environment. The pharmacological properties of the bioactives, namely anti-oxidant, anti-inflammatory, and anti-cancer activities, are reviewed. The use of citrus products and by-products as functional food additives, active packaging material, and cosmetic ingredients has been emphasized. The valorization of citrus waste for bioenergy and biosorbents is also highlighted in the review. The study also identifies the obstacles to the standardization and bioavailability of citrus by-products for the production of next-generation bioactive resources.